The present invention relates generally to driven lighting sources such as LED light fixtures. More particularly, the present invention relates to lighting control systems implementing ambient light sensors for regulating lighting output from a light fixture.
It is relatively common practice to achieve energy savings via the use of light sensors (e.g., photocells or photo-sensors) to measure natural or ambient light (e.g., sunlight) in a defined area such as a room and to accordingly adjust the artificial or electrical light. In fact, this practice is mandatory in a number of U.S. states, and is often referred to as Daylighting or Daylight Harvesting. In practice, the light sensor determines how much artificial light is necessary to maintain a desired level of illumination within the area. When there is no natural light, the light sensor will relay this information to a local or remote controller, which will signal or otherwise directly control the ballast to operate at its pre-programmed maximum level. When the light sensor detects natural light, the controller will dim the ballasts by an equivalent amount so that the total illumination of the room does not change.
There are a number of issues with the use of external photo-sensors for this purpose, including for example the cost and the undesirable size of the components as needed for mounting with respect to the light fixture. Photo-sensors also require a separate power source and a communication interface to the light fixture in order to properly regulate the driven lighting source.
For example, the most common construction method for LED modules to be used in light fixtures is mounting light emitting diode elements (LEDs) directly to a printed circuit board (PCB). Mounting an ambient light sensor on the existing PCB of an LED module would alleviate or simplify all of the issues with external photo-sensors. However, the high levels of electrical light on the LED module would make it very difficult to measure the ambient or natural light in the room directly from the PCB.